Access devices for measuring temperature of a patient

ABSTRACT

An access device such as a catheter, or introducer, or any combination of the above is provided. Within the access device is at least one lumen, channel or instrument that carries or itself is a thermally active mass, such as infusion fluids, control wires, etc. A temperature sensor such as a thermistor is secured to the access device in order to measure the temperature of a temperature medium, typically blood, in a patient. Various insulating lumens, insulating members and mounting and extrusion configurations are provided by the invention to insulate the temperature sensor thermally from the thermal mass, which might otherwise degrade the accuracy of the temperature measurement. The invention also provides an arrangement whereby the temperature sensor is connected to an external monitor for display of the patient&#39;s temperature.

RELATED APPLICATION

The present application is a continuation of U.S. Pat. No. 6,383,144,filed Jan. 18, 2000, and scheduled to issue on May 7, 2002.

FIELD OF THE INVENTION

This invention relates to methods and devices for measuring the bodytemperature of a patient in conjunction with the placement within thepatient of an access device, for example, a catheter or introducer.

DESCRIPTION OF THE RELATED ART

The needs to properly treat a patient and to gain as much information aspossible about the physiological state of a patient are often at oddswith the desire to reduce discomfort to the patient as much as possible.For example, there is frequently a need both to deliver variousmedications to a patient, and also to monitor the patient's bodytemperature. Accordingly, catheters are often inserted into thevasculature of a patient to allow delivery of various medications,hydrating fluids, etc., and to measure blood pressure. The patient'sbody temperature, however, is monitored with a separate device, which isinserted separately.

Conventional devices for measuring temperature include the well-knownoral thermometer, rectal, axillary (armpit), and tympanic (ear)thermometers and probes, as well as Foley catheters (bladdertemperature), and nasopharyngeal probes (esophagus) probes. Each ofthese devices suffers from one or more shortcomings. The firstdisadvantage is obvious to anyone who has ever been the patient: It isuncomfortable enough to have a catheter inserted into one's vein orartery without also having to have a separate device inserted into one'srectum, bladder, ear or nose, or down one's throat.

The second disadvantage has to do with accuracy—taking a patient'stemperature by placing a thermometer under her armpit or in her mouthmay cause the least discomfort to the patient, but the temperature valuethis provides is usually less accurate and much more dependent onplacement than temperature measurements of blood in a major vessel.

One way to overcome these disadvantages is to include some form oftemperature sensor within the inserted catheter itself. This allows formeasurement of the blood temperature, which is in most cases much closerto the patient's actual body core temperature. The problem then arisesthat other elements of the catheter system may have thermal propertiesthat themselves affect the temperature that the sensor senses. Thisproblem arises in the context of thermodilution systems for measuringcardiac flow. U.S. Pat. No. 4,817,624 (Newbower, 4 Apr. 1989), U.S. Pat.No. 5,176,144 (Yoshikoshi, 5 Jan. 1993), and Published European PatentApplication 0 357 334 B1 (Inventors: Williams, et al., 7 Mar. 1990) forexample, describe such systems. As is well known, in such athermodilution system, the temperature of the cardiac blood flow ismodulated according to a predetermined pattern that is created by theinjection of an indicator, which is usually either a series of bolusesof a relatively colder fluid, or heat. The downstream response to thetemperature modulation is sensed by a thermistor and is used tocalculate and estimate blood flow.

In systems such as Newbower's, temperature modulation is accomplished bycooling the blood through precisely dosed boluses of a thermallywell-controlled fluid colder than the blood. In Williams, modulatedcooling of the blood is accomplished using a heat exchange mechanismthat does not require actual injection of any bolus into the bloodstream. In systems such as Yoshikoshi's the blood is instead heatedlocally using a heating element that is mounted near the far (distal)end of a cardiac catheter. As before, a thermistor senses the downstreamresponse profile, whose characteristics are used to calculate cardiacflow.

Such thermodilution systems have certain clinical limitations, sincethey must deal with several problems specific to this application. Firstis the problem of retrograde flow: If the thermistor is located proximalto the heater or bolus injection port, then the heated/cooled blood willflow back over the catheter tip. The temperature of the catheter itself,which may contain various other lumens, injectates, control wires, etc.can then affect the temperature profile of the thermally modulated bloodand degrade the flow calculations.

To overcome this effect, the injection is replaced by a continuousinfusion of indicator in order to obtain a new steady-state baseline;however, this is an undesirable clinical limitation due to thevolume-loading the patient. Even when the thermistor is located distalrelative to the heater/bolus port, this problem may still arise.

These thermodilution system catheters normally have a distal infusionlumen that passes beneath the thermistor or temperature sensor and exitsat the tip of the catheter. Since the flow in such an infusion lumen canseverely degrade the accuracy of the temperature sensor measurements,the flow is limited to a maximum amount in order for the blood flowmeasurement to still be accurate. Of course, such a limitation oninfusion lumen flow is also undesirable from the clinical perspective.

An analogous problem of insulation arises in other cardiac devices aswell, such as the catheter-based cardiac ablation system described inU.S. Pat. No. 5,688,266 (Edwards, et al., 18 Nov. 1997). In Edwards'system, an ablation electrode is used to kill tissue locally using heat,and one or more temperature-sensing elements are used to sense thetemperature of the tissue to be ablated and allow precise control of theablation temperature and time. Isolation, provided primarily by physicalseparation, is thus required between the electrode and the temperaturesensors; otherwise, the sensors will tend to give readings that are toohigh.

At least one factor limits the use of these known systems in general usefor measuring a patient's body temperature: These systems are notarranged to measure the patient's actual, natural body temperature atall, but rather the temperature of blood or some body tissue whosetemperature the system itself has deliberately altered.

There are other devices, such as central venous catheters (CVC),peripheral catheters, and other catheter-like instruments such asintroducers. As their names imply, such catheters do not requireplacement into the heart and are consequently used more frequently indifferent areas of the hospital. Unlike cardiac catheters, which areoften more than 100 cm long and require an introducer for insertion,these devices are seldom longer than about 20-30 cm and can be insertedby the Seldinger technique. A CVC, for example, is often placed in apatient's jugular vein and is used for various infusions, for monitoringblood pressure, etc., through a number of lumens within the device.

An instrument such as a CVC often includes several different lumenswhich may carry a range of fluids (such as medications and otherinfusions), as well as instruments such as pressure transducers. Each ofthese fluids and instruments may be at different temperatures, or mayhave varying thermal properties, or both. Any measurement of temperatureusing such a catheter would thus risk serious thermal contamination fromother portions of the catheter.

There are at present no known devices such as a CVC, peripheralcatheter, or introducer that incorporate an arrangement for measuringblood temperature accurately. Therefore, it would be advantageous to beable to accurately measure temperature in conjunction with such accessdevices as catheters and introducers while eliminating the need toinsert a secondary device into the patient in order to measuretemperature, as is the current practice. Such devices would also providea more accurate and less time-consuming body temperature measurementthan non- or less invasive devices. This invention provides such anarrangement.

It would also be advantageous to be able to connect a CVC or similarcatheter to a standard patient monitor. Not only would this bring theobvious benefit that the patient's temperature could be viewed at aglance along with other monitored parameters, but it would also make thetemperature values available for other processing as needed. Manypatient monitors, however, use a signal standard that is compatible withlarge thermistors or temperature sensors and not compatible with theoutput of miniature temperature sensors used on pulmonary arterycatheters. The use of miniature thermistors is desirable because itallows for catheter sizes to be relatively small. One could of coursereprogram the monitors, but such a solution to the problem would becostly and complicated, and may not be possible or practical in existingmonitors. This invention provides an arrangement that allows acatheter-based temperature sensor to be connected to existing monitors.

An additional issue is that many patients, as their condition improves,do not require continuous monitoring of temperature, and therefore, donot require a dedicated connection between the catheter(s) and themonitor. At present, the dedicated connections limit how many patientsthe system can monitor, and increases the number of cables andconnectors needed. It would be advantageous to free the system to allowmonitoring more that one patient. This would, for example, enable nurseor physician to have a quick look at the patient's temperature, possiblyenter it into the patient's chart, and then move on to other tasks orpatients. It would therefore be beneficial to have an arrangement thatprovides this flexibility and simplicity. This invention does this aswell.

SUMMARY OF THE INVENTION

In general, the invention provides an access device, such as a catheter,an introducer, or combination of catheters, introducers, probes and thelike, that allows more accurate sensing of body temperature, forexample, of a temperature medium such as blood, by insulating atemperature sensor from thermal contamination caused by a thermal mass,such as an infusion fluid or an instrument, introduced in portions ofthe access device. In the preferred embodiment of the invention theaccess device is a central venous device that includes a temperaturesensor such as a thermistor, a thermocouple, etc.

The access device is insertable into the patient at a location of thetemperature medium, and the access device includes at least one thermalmass other than the temperature medium. The access device supports thetemperature sensor and includes at least one insulating structureinsulating the temperature sensor from the thermal mass.

In certain embodiments of the invention, each thermal mass is locatedwithin a thermal lumen within the access device. The temperature sensormay be mounted externally to an outer surface of the access device, orwithin a sensor lumen of the access device. The insulating structurepreferably extends between the temperature sensor and each thermallumen.

The temperature sensor may also be mounted in or on a carrier. Theinsulating structure is then preferably formed as a barrier within thecarrier and the carrier is held in one of the lumens of the accessdevice with the barrier extending between the temperature sensor and thethermal lumen. The carrier may be removably insertable in the lumen ofthe access device.

In other embodiments of the invention, a pair of ports is formed in anouter wall of the access device and a flow channel is formed within theaccess device and extends between the pair of ports. The temperaturemedium, such as blood, then occupies the flow channel. The flow channelis located between the temperature sensor and the thermal lumen, orbetween the insulating structure and the thermal lumen, and thereby notonly increases thermal contact between the temperature sensor and thetemperature medium, but it also thermally isolates the temperaturesensor further from the thermal lumen. The flow channel may thus itselfform the insulating structure.

In another embodiment of the invention, the access device has an openingin an outer wall and the temperature sensor, when in a deployedposition, extends into the opening. This increases thermal contactbetween the temperature sensor and the temperature medium and furtherinsulates the temperature sensor from the thermal mass. If thetemperature sensor is mounted on a carrier, then ends of the carrier maybe secured within the access device. The carrier is then positionedbetween the temperature sensor and each thermal lumen, thereby formingthe insulating structure.

The temperature sensor may alternatively be mounted within the carrier,which then protrudes as a loop out through the opening in the outer wallof the access device. The ends of the carrier are then preferablysecured within the access device. In this embodiment, the insulatingstructure comprises a flow channel for the temperature medium, which isformed between the carrier and the access device at the position of theopening, and thus between the temperature sensor and the thermal mass.One advantage of this embodiment is that the temperature sensor isexposed substantially over its entire outer circumference to thetemperature medium, via only the carrier.

Alternatively, the temperature sensor may be a right-angle thermistormounted to extend out of the opening mainly perpendicular to a centralaxis of the access device.

In another embodiment of the invention, the temperature sensor isadhesively attached to the access device. The adhesive may bedissolvable at body temperature, so that the temperature sensorseparates from contact with the access device when in position withinthe patient.

The access device may include a plurality of lumens, whereby thetemperature sensor is mounted within a recess in an insulating member.The insulating member, together with the temperature sensor, are thenmounted within one of the lumens of the access device so that theinsulating member extends between the temperature sensor and the thermallumen.

In another embodiment of the invention, the insulating structureincludes an insulating material that is co-extruded with the accessdevice and surrounds either at least a portion of each thermal lumen, orthe temperature sensor itself.

In yet another embodiment of the invention, the access device has alumen and a sensor port and the temperature sensor is mounted on adistal tip of a separate device, for example, a probe. The probe isinsertable into the lumen of the access device so that the temperaturesensor extends through the sensor port.

The insulating structure may also comprises a distal tip of the accessdevice itself. The tip is then preferably formed from an insulatingmaterial as a separate member, and the temperature sensor is mountedwithin the distal tip. Alternatively, the distal tip of the accessdevice may be provided with a lengthwise extending slit. The temperaturesensor is then mounted on a first side of the distal tip and at leastone thermal lumen carrying the thermal mass extends through a secondside of the distal tip. The distal tip, in a deployed position, thenseparates along the slit, with the first and second sides of the tipbeing located on either side of the slit.

In another embodiment of the invention, the insulating structure is alumen or a chamber in the access device that is expandable to increasethe distance between the temperature sensor and the thermal mass.

The access device according to the invention is preferably included as asensing member in a more general system for monitoring the bodytemperature of a patient. In this system, the access device isinsertable into the patient and is connected to a temperature monitorthat converts a sensor output signal of the access device into a patienttemperature signal and for displaying the patient temperature signal. Aconnector is then provided to connect the temperature sensor with thetemperature monitor.

The system according to the invention preferably further includes anadapter in the temperature monitor. The adapter converts the sensoroutput signal into a predetermined display format. The temperaturemonitor may also be provided with a display and a power supply, in whichcase the entire monitoring system may be implemented as a hand-held,self-contained unit that is portable between different patients.

The invention also encompasses a method for measuring the bodytemperature of the patient. The main steps of the method according tothe invention involve supporting the temperature sensor on the accessdevice; inserting the access device into a blood vessel; introducing atleast one thermal mass into the access device; and insulating thetemperature sensor from the thermal mass. In the preferred methodaccording to the invention, the thermal mass is introduced via a thermallumen located within the access device. One then mounts the temperaturesensor in a sensor lumen within the access device and forms at least onethermally insulating structure between the temperature sensor and thethermal lumen. In some embodiments, to provide the thermally insulatingstructure, one may introduce a thermally insulating material into alumen within the access device.

The invention also comprises a method for manufacturing the accessdevice. In the preferred embodiment, this method comprises extruding theaccess device, forming a thermal lumen through which a thermal mass isintroduced, forming a sensor lumen through which a temperature sensor isintroduced, and forming an insulating structure separating the sensorlumen from the thermal mass. In manufacturing the access device, thetemperature sensor may be mounted in the sensor lumen at a distal end ofthe access device. A signal wire is then drawn from the temperaturesensor to an external patient monitor.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates one example of an access device according to theinvention, such as a CVC catheter, that is inserted into a patient'svein for measuring temperature.

FIG. 2 illustrates another example of an embodiment of the invention inwhich a temperature sensor is located within a lumen of a catheter butis thermally insulated from other lumens by an insulating gap.

FIG. 3 a illustrates a temperature sensor that is provided within adedicated tubular member that also includes a built-in insulating lumen.

FIG. 3 b shows the lumen of FIG. 3 a in place in the catheter.

FIGS. 4 and 5 show embodiments of the invention in which blood isallowed to flow past the temperature sensor in place in the catheter,with and without an insulating gap being provided between thetemperature sensor and catheter lumens.

FIGS. 6 a and 6 b are side and end views, respectively, of anotherexemplary embodiment of the invention in which the temperature sensor ismounted on an insulating member, whereby both are inserted into the samecatheter lumen.

FIGS. 7 a and 7 b are side and end views, respectively, of an embodimentof the invention in which the temperature sensor is mounted on the outersurface of the catheter.

FIGS. 8 a and 8 b are side and end views, respectively, of anotherembodiment of the invention in which the temperature sensor is mountedto extend out from the outer surface of the catheter, with a blood flowchannel located between the temperature sensor and the outer surface.

FIG. 9 illustrates an embodiment of the invention in which thetemperature sensor is a right-angle thermistor extending through anopening in the outer surface of the catheter to provide surface contactbetween the temperature sensor and the blood.

FIGS. 10 a and 10 b illustrate an embodiment of the invention in whichthe temperature sensor is mounted on an a separate insulating memberthat can be inserted along with the sensor into a catheter lumen.

FIG. 11 illustrates an embodiment of the invention in which thetemperature sensor is mounted on the tip of a probe that can be insertedinto an access device such as a catheter.

FIGS. 12 a and 12 b illustrate embodiments of the invention in which aninsulating material is co-extruded with the catheter itself.

FIGS. 13 a and 13 b illustrate another embodiment of the invention, inwhich the temperature sensor is mounted within a catheter tip that isinitially formed as a member separate from the catheter body itself.

FIGS. 14 a and 14 b illustrate still another embodiment of theinvention, in which the distal tip of the catheter splits after it isplaced within the patient, with the temperature sensor and catheterlumen(s) containing thermal mass then deployed on either sides of thesplit.

DETAILED DESCRIPTION

In broadest terms, this invention provides an arrangement or a device inwhich a temperature sensor is used with an access device, preferably avascular access device, for insertion into the body of a patient. Thisinvention also provides various insulating structures that reducethermal contamination of the temperature sensor from other portions ofthe interior of the access device. The temperature sensor is designed tosense some temperature medium within the patient's body, for example,blood.

One example of the preferred access device of this invention is acentral venous catheter (CVC), but it could be some other instrumentthat also carries or includes fluids or other devices—cumulatively“thermal masses”—that could affect the temperature at the temperaturesensor. Examples of other access devices include peripheral catheters,introducers, obturators, and probes. In fact, the term “access device”also contemplates any combination of these devices, such as acombination of one or more introducers, catheters and probes. Forexample, a catheter is often inserted within an introducer, and eitheror both could be arranged according to suitable embodiments of theinvention to improve the accuracy of temperature measurements.

In the context of this invention, a thermal mass is any substance orstructure carried within the access device that has or could have atemperature and heat capacity such that heat flow into or out of themass could significantly affect the sensed temperature. Here,“significantly” means so much that the temperature measurement would notbe acceptably accurate for clinical use.

As used in this invention an “insulating structure” is any structurethat insulates the temperature sensor from a thermal mass. As isdescribed and illustrated below, insulating structures used in theinvention, include, but are not limited to, a device lumen or anyportion of a device lumen, a channel, a gap, a chamber or just an areaprovided immediately surrounding the temperature sensor. An insulatingstructure may also include an insulating material, for example, aceramic, or a separate device such as a probe that is inserted into orthrough the access device.

The examples of suitable access devices described below are preferablymade of biocompatible polymer materials, since in most cases they willbe inserted at least partially into a patient. Polyurethane is the mostcommon material, since it meets all normal requirements for thermal andmechanical stability when in a patient; PVC and Teflon are alsoacceptable, as well as other conventional materials. The access devicesfor use with this invention may, moreover, be made of an anti-microbialmaterial or may be covered with material or coating havinganti-microbial or thromboresistant properties.

The temperature sensor used in this invention may be any conventionaldevice. The most easily implemented sensor is a thermistor, which issmall, widely available and relatively easy to calibrate. Othertemperature sensors may, however, also be used. Alternatives includeconventional thermocouples and fiber optic temperature sensors. The onlyrequirement is that the sensor should predictably change a measurablephysical property, such as its electrical resistance or opticalspectrum, in response to changes in temperature, and this change shouldbe detectable externally via an electrical or optical conductor in sucha way that temperature can be converted to an electrical signal. Thesedevices, and the way in which their signals are conditioned for furtherprocessing are well known.

In the following discussion of the various exemplifying embodiments ofthe invention, it is assumed merely by way of example that the accessdevice is a CVC, that the temperature sensor is a thermistor, that thecatheter is inserted into a body vessel, such as a vein, and that thetemperature medium whose temperature is to be determined is blood. Theinvention will work just as well with other access devices and sensors,insertion points, and temperature media, as will be obvious to thoseskilled in the art.

FIG. 1 illustrates the general structure of the invention. A catheter100 is inserted into a patient's vein 110 in the conventional manner.Arrows within the vein 110 indicate flowing blood. A thermistor 120 ispositioned at the distal end of the catheter, which includes lumens,channels or tubes through which fluids can be infused into the patient,or which hold other instruments. Two conventional infusion connectors130, 132, are shown inserted into respective lumens in the catheter. Thenumber of lumens and connectors will of course depend on the particularcatheter used and the application. The invention will work with anynumber of lumens or internal channels in the catheter.

A conductor (shown as the dashed line 125), which forms a signal wire,connects the thermistor electrically (or optically, depending on thetype of temperature sensor used) with external conditioning, processingand display circuitry 150. In FIG. 1, this exemplary circuitry is shownas including a signal adapter 160 and a patient monitor 170, with aconventional electrical coupler 180 and a guide tube 185 connecting thethermistor signal wire 125 to the external circuitry 150. A conventionalpower supply 172 is also included, as is a temperature display 174,which may be either a separate display device or simply a portion of anexisting monitor display. These features, some of which are optional orcan vary depending on the embodiment, are described below in greaterdetail. Any conventional devices and circuits may be used to communicatethe thermistor's 120 output signal to external monitors or displays.

FIG. 1 also shows a section line A-A. The description of variousembodiments of the catheter according to the invention is illustrated bycross-sectional drawings. Line A-A is the reference line for thesecross-sectional views.

FIG. 2 illustrates one exemplifying embodiment of the invention. In thisembodiment, the thermistor 120 is located within a dedicated opening orlumen 210 within the catheter 100. In this figure, the thermistor lumen210 is shown as being mainly circular. This is not necessary; anyappropriate and desired lumen shape may be used. A circular or at leastrounded lumen cross section will in most cases be preferable, however,since standard thermistors frequently are provided as glass-encapsulatedbeads with a mainly round cross section. Three other lumens 220, 222,224 are also illustrated (however, any number of lumens may beincluded).

Assume now that one or more of the lumens 220, 222, 224 carries somefluid (or contains some instrument) with a thermal mass and temperaturethat could affect the temperature measured by the thermistor 120. Forexample, an infusion fluid might be administered through the lumen 220.If the temperature of the fluid is above or below that of the patient'sblood, then it could influence the temperature measurement because ofthe thermal conductivity of the catheter material between the thermistorand the fluid. An additional insulating structure, such as a lumen orgap 250 is therefore preferably extruded in the catheter so as toextend, for example, laterally between the thermistor and all the otherlumens 220, 222, 224.

The insulating lumen (gap) 250 is preferably as wide and thick aspossible to maximize the degree of thermal insulation of the thermistor,given the minimum permissible material thickness required to maintainstability of the catheter and lumen walls, as well as the maximum outerdiameter of the device. The minimum distance between the thermistorlumen 210 and the outer surface of the catheter 100 is, however,preferably as small as possible to ensure the best thermal contactbetween the thermistor and the surrounding blood.

The insulating structure, such as the lumen or gap 250 of FIG. 2 ispreferably filled with air, or with some other conventional gas, ceramicpellets, a conventional high-impedance gel, etc., to additionallyincrease its thermal impedance. The insulating material may also be astrip or layer or similar separate piece of an insulating material thatis inserted into the lumen 250. This insulating material may optionallybe bonded to the catheter in any known way. The most distal end of theinsulating lumen is preferably sealed to prevent inflow of blood andoutflow of the thermally insulating gas or other insulating material.

In FIG. 2, only one insulating lumen is shown. This is by way of exampleonly. More than one gap may be created, space permitting, to extendbetween the thermistor and the other lumens to further increase thethermal isolation of the thermistor. Also, the insulating lumen may beof any length—it may extend through the full length of the access deviceor any appropriate portion of its length. For example, a portion of thelumen 250 may be used as an infusion or device lumen for introduction ofmedications or guidewires. A plug may be placed somewhere along thelength of such lumen to block off the remainder of the infusion/devicelumen so that the remaining portion will act as an insulating structure.The location of the plug must be selected such that the blocked offportion of the infusion/device lumen will be adjacent to the location ofthe temperature sensor. It will be necessary to provide a side portprior to the location of the plug to allow the infusion/device to exitthe access device.

The lumen(s) 250 also does not need to be shaped as a generallylaterally extending slit, as shown in FIG. 2, although this typicallymaximizes the isolation of the thermistor from the other lumens.Instead, lumen 250 may be shaped as half-moon or be concentric with thethermistor lumen, or otherwise extruded so as to surround the thermistorlumen 240. Also, the gap could be created by several mainly cylindricalor otherwise curved lumens spread out between the thermistor and theother lumens 220, 222, 224.

In yet another variation of the insulating lumen 250 it—that is, thecatheter material around and defining it—is made elastic enough that thelumen 250 is inflatable after the catheter is inserted into the patient.For example, the lumen 250 could be formed to have flexible webs. Oncethe catheter is inserted, any suitable pressurizing material, such asair, an inert gas, foam, or some other known thermal resistance materialcould be pumped into the lumen 250, causing its cross-sectional area toexpand and increase the gap or distance between the thermistor andthermal masses. The embodiment facilitates easy insertion of the deviceby keeping its outer diameter small, since the insulating lumen orstructure is expanded only after the device is in place.

The lumens 220, 222, 224 may be used for any conventional purpose. Anyor all of them may, for example, carry fluids, or act as channels forguiding other instruments such probes, pressure transducers, etc. Ofcourse, they need not all have the same function—one lumen might becarrying an infusion fluid while another is a channel for an instrument.

FIGS. 3 a and 3 b illustrate an embodiment of the invention in which thethermistor 120 and a thermally insulating lumen/gap 350 are provided ina separate mainly tubular member 300 which may be inserted into anexisting lumen 310 or channel within the catheter 100. The tubularmember 300 is preferably made of the same—or at least same type ofmaterial as the catheter itself, that is, a thermally stable,biocompatible polymer such as polyurethane. This material requirement isnot as strict as for the catheter itself, however, since the tubularmember is mounted within the catheter. The gap 350, which may be filledwith further insulating materials as described above for the lumen 250,is then oriented within the lumen 310 so as to extend between thethermistor and other lumens 320, 322, 324, 326 within the catheter. Inorder to provide proper orientation of the tubular member within thelumen 310, a key (not shown) such as a rod shaped to conform to the gap350 could be provided, if needed. The user can then first insert themember 300, with the thermistor, into the lumen 310 and then insert thekey into the proximal end of the gap 350 and turn the member 300 intoproper alignment.

FIGS. 4 and 5 illustrate embodiments of the invention in which blooditself is channeled between the thermistor 120 and one or more otherlumens 424, which may be carrying sources of thermal “noise” such asinfusion fluids. In these embodiments, ports 410, 412 are formed inmainly diametrically opposing portions of the outer wall of the catheter100 and a channel is formed (as part of the normal extrusion between thetwo ports). The ports 410, 412 may be arranged anywhere along thecircumference of the catheter wall—not just diametrically opposing—aslong as blood can flow between the temperature sensor and the thermalmasses. In FIG. 4, the channel has three chambers—two outer chambers440, 444 and an intermediate chamber 442—through which blood can flow(indicated by arrows passing though the channel). Note that the ports410, 412 need be formed only in the region of the thermistor 120, andcan thus be simple holes or slits cut in the catheter wall. The channelmay be formed as a small chamber or it may extend over any length of thecatheter as a result needed to simplify the extrusion. Note that a CVCor peripheral catheter, unlike a cardiac catheter, is typically no morethan about 30 cm long, so it will in general not be a problem to let thechannel extend as far as the other lumen(s) 424.

In the embodiment of the invention shown in FIG. 4, the blood isdirected to a region—the intermediate chamber 442—immediately adjacentto (that is, extending just under, viewed as in FIG. 4) the thermistor120; the maximum distance separating the thermistor from blood whosetemperature is to be measured both above and below can be made as littleas the minimum structurally allowable thickness of the cathetermaterial. The blood thus not only helps isolate the thermistor from thelumen(s) 424, but it also better contacts the thermistor thermally,since it does so from two sides instead of just one. A central ridge ortab 470 may be extruded to extend between the two outer chambers 440,444 and from the lumen 424 toward the thermistor, in order not only todirect the inflowing blood past the thermistor, but also to reduce theamount of blood within the catheter while still allowing for aninsulating layer of blood to flow between the thermistor and thelumen(s) 424. The ridge is, however, not necessary to this embodiment ofthe invention.

In the embodiment of the invention illustrated in FIG. 5, the chambers440, 444 and 442 and the ridge 470 (FIG. 4) have been eliminated.Instead, the intermediate chamber 442 is sealed off from the blood flowand thus forms an insulating gap or lumen 550, similar to the lumen/gap250 in FIG. 2. In this embodiment, the blood flowing through the singlechannel 540 serves mainly to isolate the thermistor thermally from thelumen(s) 424. The lumen/gap 550 provides an additional insulatingbarrier, although it is not required, especially if the flow of bloodthrough the channel is fast enough to preclude significant heat transferto or from the thermal mass from which the channel separates thethermistor. Note that another advantage of the embodiment shown in FIG.5 is that the blood in the channel 540 also tends to bring thetemperature within the gap 550 to blood temperature and thus furtherinsulates the thermal mass.

In the embodiments of the invention shown in both FIGS. 4 and 5, thechannel 540 may be a limited chamber located near the thermistor itself,or it may be a lumen passing through any portion of the length of theaccess device. In either case, the channel 540 itself (with passingblood) serves as an insulating structure.

FIGS. 6 a and 6 b are a partially cut-away, side view and an end view,respectively, of another embodiment of the invention in which thethermistor 120 is mounted on a carrier 600, which is preferably made ofa biocompatible material and also provides improved thermal insulation.It may be made, for example, of plastic, metal or ceramic. Thethermistor may be mounted securely onto the carrier using anyconventional material such as a standard adhesive such as pottingcompound or a non-toxic, moisture-proof, thermally stable glue.

In this embodiment a port is formed as a cut-away opening 605 in theouter wall of the catheter 100. The thermistor is then positioned so asto lie within the opening in the catheter and thus be exposed directlyto the blood over most of its surface are, without any portion of thecatheter in between. The thermistor's signal wire 125 is also shown inFIG. 6 a.

The thermistor 120 and its carrier 600 may be inserted into an existingor dedicated lumen 610 in the catheter so that the carrier extendsbetween the thermistor and other lumens 620, 622 or thermal noisesources in the catheter. Note that the opening 605 preferably extendsinto the lumen 610 to ensure maximum direct contact between thethermistor and the surrounding blood.

The thermistor and carrier 600 may be inserted into the catheter withthe thermistor in position in the opening 605 before the catheter isplaced within the patient. Alternatively, before insertion, and assumingthe carrier is made of a sufficiently flexible material, the thermistorand the far, distal end of the carrier 600 could be allowed to stick outof the opening 605, preferably bent back along the catheter wall andpointing away from the direction of insertion. Once thermistor catheteris placed in the patient, the physician could then pull on the proximalend of the carrier until the thermistor is pulled into place in theopening 605. The distal end of the carrier can then be made short,extending only a short distance from the thermistor, so that only itsproximal end would be within the catheter. The carrier, which may betubular, then forms an insulating gap beneath the thermistor, similar tothe gaps 250, 350 and 550 in previous embodiments described above.

FIGS. 7 a and 7 b are a partially cut-away, side view and an end view,respectively, of an embodiment of the invention in which the thermistor120 is mounted on the outer wall of the catheter 100 itself. In order toavoid having the thermistor's signal wire or fiber 125 running along theouter surface of the catheter to the exterior, it is pre-threaded intothe catheter 100 through a small hole 705 made in the catheter wall,preferably just behind (proximal relative to) the thermistor 120. Thethermistor may be mounted securely onto the catheter using anyconventional method or material such as a standard potting compound 710,or a non-toxic, moisture-proof, thermally stable glue, or a liquefiedsolution of the catheter material that would solvent bond to thecatheter tubing. The potting compound should be spread to cover the hole705 and at least most of the thermistor, but not so thickly over thethermistor as to interfere with its ability to quickly and accuratelyrespond to temperature changes. In order to reduce the maximum diameterof the catheter and thereby make insertion easier, an indentation couldbe made in the outer wall of the catheter. The thermistor can then bemounted on the catheter by potting it securely in the indentation (notshown).

In the embodiment of the invention shown in FIGS. 7 a and 7 b, it wouldalso be possible to mount the temperature sensor using a non-toxicpotting material (or other adhesive) that dissolves when exposed to theblood. Once the catheter is in place, the potting material wouldtherefore dissolve. This would expose the temperature sensor directly tothe blood and thus allow for even more accurate temperaturemeasurements. Moreover, the temperature sensor will then tend toseparate and move away from the outer wall of the catheter, therebyfurther insulating it from any thermal masses within the catheter.

This “deployment” action may also be arranged by providing the signalwire with an elbow joint made of a memory metal that is straight(extending in the direction of the catheter) during inserting but thatis bent in the relaxed state—when the potting compound dissolves, thejoint would relax and bend, thus moving the temperature sensor out fromthe catheter wall. If it is not practical to form this memory elbowjoint in the sensor's signal wire itself, then a piece of memory metalcould be attached to the wire where the elbow joint is needed. Thesensor could then also be potted within an indentation such as in FIG. 6a, so that the catheter could have an outer surface free of protrusions.

As FIGS. 7 a and 7 b show, several lumens 700-705 or tubular members arepreferably included within the catheter in order to provide insulatinggaps between the externally mounted thermistor 120 and the lumen(s) thatcarry infusions. A single lumen/gap such as the lumen 250 shown anddescribed in reference to FIG. 2, or a blood channel similar to thechannels shown in FIGS. 4 and 5 may be included instead of or inaddition to the lumens 700-705 to further insulate the thermistorthermally from the lumen 724.

FIGS. 8 a and 8 b are a partially cutaway, side view and an end view,respectively, of an embodiment of the invention in which the thermistor120 is mounted within a short tubular member 800 that protrudes outthrough an opening 805 made in the outer wall of the catheter 100. Thetwo ends of the tubular member 800 are secured within the catheter usingany known technique. A channel 810 is thereby formed between the “loop”of the tubular member 800 and the catheter. Blood will therefore be ableto flow substantially completely around the thermistor 120 and will alsoisolate the thermistor thermally from any interior lumen(s) 824 withinthe catheter. During insertion of the catheter, the member 800 willpreferably lie flat, that is, mostly straight, within the catheter.

Once the catheter is in place, the physician could then insert thethermistor, for example by pushing it in with a wire, and could thenpush the thermistor and loop of the member 800 out through the opening805 to deploy the temperature sensor, that is, the thermistor. One wayto do this would be to insert a separate instrument that has a bend onit into, for example, a lumen in which the member 800 lies (or simplythe interior of the catheter). Twisting the instrument with the bendunder the thermistor would then push it out through the opening 805.Alternatively, if the far distal end of the tubular member 800 is fixedin the catheter, and if the member 800 is not too flexible, then itwould push out through the opening by the physician pushing the proximalend inward.

FIG. 9 illustrates an embodiment of the invention in which thethermistor 120 is a right-angle device, that is, there is asubstantially right-angle bend in the rod or wire that connects it toits signal wire 125. Of course, angles of bend other than 90° may alsobe used—the proper angle of bend will depend on the particularimplementation and may be determined using known methods. Thisright-angle thermistor 120 is then potted securely in an opening 905,similar to the openings 605 and 805, formed in the catheter wall, sothat the thermistor extends outward approximately perpendicular to thedirection of longitudinal extension (central axis) of the catheter. Asbefore, the minimum amount of potting compound should be used to securethe thermistor, since this will also minimize the impact caused by thecompound itself on the thermistor's ability to sense blood temperature.As before, one or more insulating lumens 900 may also be included in thecatheter to isolate the thermistor from fluid-carrying lumen(s) 924.

FIGS. 10 a and 10 b are a rear and an elevated side view, respectively,of an embodiment of the invention in which the thermistor 120 is mountedso as to lie within a recess in a separate insulating member 1000, whichis shaped generally as a partially hollowed out cylinder with a closed,rounded, smooth leading surface and a slot 1010 into which thethermistor can be laid for mounting. The insulating member should bemade of a smooth, thermally insulating material such as ceramic, metal,foam or Teflon. Polymers such as polyurethane may also be used, whichwould make it possible to injection-mold the member 1000. Theinsulator/thermistor sub-assembly is then inserted, for example, bypushing it in with a rod, into a suitable catheter lumen, such as thelumens 210, 310, 610 shown above for other embodiments of the invention.The slot should thereby be oriented, for example, using a key or similartool, away from other catheter lumen(s) that carry thermal masses suchas fluids and instruments.

In FIG. 11, an embodiment of the invention is shown in which thetemperature sensor 120 is mounted on the tip 1110 of a separate device,for example, a guidewire or a probe 1100, which can be inserted into theaccess device 100. To deploy the sensor 120, once the access device isin place, the tip of the probe is inserted into a lumen of the device100 and is then pushed in until the probe tip 1110 protrudes from a port1140 that is either cut in the side wall of the catheter (as in some ofthe other embodiments described above), or is simply the innermostopening of the lumen in which the probe is inserted 1142. (Alternativeexit of the tip of the probe is shown as a dashed line.) The probe thusitself acts as a structure that separates (and thus insulates) thetemperature sensor from thermal masses. The tip of the probe ispreferably curved to a mainly “J”-shape so that it will more easilyextend through the port 1140 and away from the thermal influence of theparts of the access device; however, a straight tip is also acceptable.One advantage of this embodiment of the invention is that it could beinserted only if needed, in which case it can be sealed against bloodleakage by a conventional hemostasis valve.

FIGS. 12 a and 12 b illustrate embodiments of the invention in which aninsulating material is co-extruded with the catheter itself. In FIG. 12a, the insulating material 1200 is extruded along with the catheter 100so as to surround an infusion (or instrument-carrying) lumen 1210 or,alternatively, at least a portion of it near the location of thetemperature sensor. The insulating material, which may be of any knownextrudable type then acts as a thermal barrier between the contents ofthe lumen 1210 and the temperature sensor 120. In FIG. 12 b, theinsulating material is co-extruded with the catheter so as to form abarrier layer 1220 that surrounds and thereby insulates the temperaturesensor 120 itself.

FIGS. 13 a and 13 b illustrate yet another embodiment of the invention,in which the temperature sensor 120 is mounted within a catheter tip1300 that is initially formed as a member separate from the catheterbody 100 itself, but is attached or bonded to the distal end of thecatheter using, for example, a conventional adhesive. A lumen orthrough-hole 1310 is then formed in the tip 1300 to act as an extensionof any appropriate and desired lumen within the main catheter body 100to allow uninterrupted flow. The tip 1300 in this embodiment may then bemade entirely of a highly insulative material. This completely avoidsthe need to extrude the insulating member over much or even the entirelength of the catheter. It also makes possible the use of differentmaterials in the insulating member and the main catheter body with noneed for co-extrusion and without using more expensive material for theentire device.

FIGS. 14 a and 14 b illustrate still another embodiment of theinvention, in which the distal tip of the catheter 100 has a slit 1400.The temperature sensor 120 is mounted on or in the distal tip on oneside of the slit, whereas the lumen(s) 1410 carrying the thermal massextend through the tip on the other side of the slit. In short, in thisembodiment, the distal tip of the catheter splits after the device isplaced within a patient. Before insertion into the patient, the cathetertip 1300 is held together either mechanically, for example, with aninternal catch that can be released using a wire that extends out of theproximal end of the catheter, or using an adhesive that dissolves whenexposed to blood, or any other appropriate method. While in place, theslit 1400 opens to form an insulating gap (as shown in FIG. 14 b)between the thermistor 120 and the thermal masses in the lumen(s) 1410.

Several different embodiments of the invention are described above.Common to all of the embodiments, however, is that they implement themethod according to the invention by which the body temperature of apatient is sensed by a temperature sensor supported by an access device.As used here, the term “supported” means that the temperature sensor maybe mounted on or within the access device; it may be permanently affixedto or within the access device; or it may be removably connected to orinserted into the access device. The term also includes any arrangement,as described for example in reference to FIG. 11, in which a temperaturesensor is located on a separate device, which is inserted into andextended through the access device.

The access device is inserted into a patient, for example, into a vein,and at least one thermal mass is introduced into the access device. Thetemperature sensor is insulated thermally from the thermal mass. Asignal wire is led from the temperature sensor to an external patienttemperature monitor.

The invention also encompasses the method of manufacturing the accessdevice. In most of the embodiments described above, this manufacturingmethod involves extruding the access device with a plurality oflumens—one lumen through which a temperature sensor is introduced and asignal wire is led (a sensor lumen), and at least one other lumen forcarrying or guiding the thermal mass. The manufacturing method alsoincludes the step of forming an insulating structure that thermallyseparates the temperature sensor from the thermal mass. The temperaturesensor may be permanently or removably mounted at a distal end of thesensor lumen. The temperature sensor may be also mounted in a separatecarrier which is placed in the sensor lumen. The manufacturing methodmay include some other or additional steps according to the embodimentsdescribed above, as will be understood by those skilled in the art.

Refer once again to FIG. 1. The output signal from a conventionaltemperature sensor such as the thermistor 120 has well-knowncharacteristics. In general, the output signal is a voltage or currentsignal whose amplitude is functionally related to the temperature of thesensor. Moreover, the functional relationship between sensor temperatureand the amplitude of the output signal may be linear, but seldom is. Infact, most temperature sensors are individually calibrated by themanufacturer, or require calibration by the user before actual use.However obtained, there is, though, a functional relationship.

Furthermore, in some cases, the temperature output signal may becompatible with input signals of existing patient monitors, but this isnot always the case. As a simple example, amplification (scaling) andimpedance matching (or impedance isolation) are often required toconvert the output signal into a signal form and type that can beprocessed and displayed for the user.

According to the invention, the functional relationships a) betweensensor temperature and the sensor output signal, on the one hand; and b)between output signal characteristics (such as impedance, amplituderange, and whether in the form of a voltage or current) arepredetermined in any conventional manner (for example, through normalcalibration or by accepting the manufacturer's calibration data). Thesignal conditioning necessary to implement the relationships is thenimplemented in the adapter 160. The conditioned signal is then appliedto the monitor 170 for processing (if needed) and display.

In some cases, the only signal conditioning required is scaling. Thiscan be done using a conventional resistive network, with the sensoroutput signal forming the input and the system output signal being takenfrom an appropriate point in the network. Conventional passivecomponents may then be used to provide any necessary furtherconditioning such as impedance matching. This has the advantage ofimplementing the adapter 160 as a totally passive device. In othercases, conventional active components such as operational amplifierswith known resistive, capacitive and inductive feedback and feedforwardelements may be used to implement the signal conversion.

In many cases, the relationship between sensor output and temperaturemay be too irregular to implement accurately using purely passive oranalog components. In these cases, the adapter may be implemented byincluding in the adapter 160 a conventional analog-to-digital converter(ADC), a microprocessor, and a memory; note that a single conventionaldigital signal processor combines all these features in one componentand may therefore in many applications be a suitable implementation. Therelationship between the sensor output and temperature can then beimplemented as a look-up table in memory, or as parameters of anapproximating function. Using known methods, the microprocessor may thentake as an input to the lookup table or approximating function thesensed and ADC-converted sensor output signal and generate thecorresponding temperature signal, which, after any further conventionalconditioning, is applied to the monitor 170.

In one embodiment of the invention that is particularly useful in a busysetting where only a quick and easy look at a patient's temperature isneeded, the entire conditioning, processing and display circuitry 150 isincluded in a single hand-held unit. In this case, the power supply willtypically be batteries and the monitor may be as simple as aconventional, low-power LCD display (along with conventional drivingcircuitry) showing temperature to, say, single decimal precision.

Using such a self-contained, handheld device, a nurse would connect thedevice to the temperature sensor by attaching the cable 190 to theconnector 180, and the patient's temperature would then be displayed onthe display 174 in a predetermined format. The connector 180 ispreferably a conventional device such as a male/female plug pair thatwould allow the nurse to quickly connect and disconnect the device forreadings from different patients. This would allow the nurse to takereadings of many patients' temperatures quickly, with no need to waitfor a conventional thermometer to stabilize, and with little discomfortto the patients themselves. Indeed, the nurse could take an alreadycatheterized patient's temperature while he is asleep.

Assuming sufficiently powerful batteries, the self-contained embodimentof the system 150 could also include not only a memory, but also asimple input device such as a button connected to an internal electricalswitch. Whenever the nurse presses the button, the instantaneousmeasured temperature is stored in the memory portion designated for apredetermined number of values for the patient. A time stamp of themeasurement could also be generated using known techniques and storedalong with each stored temperature measurement. By later recalling thestored values, for example by pressing the button according to somepredetermined pattern, the nurse could then view the patient's recenttemperature history. The software and hardware components needed toimplement this one-button storage and recall system, even classified forseveral different patients, may be similar to those used, for example,in conventional electronic hand bearing compasses found on manywell-equipped sailboats.

As an additional feature, the hand-held system could be provided withconventional circuitry enabling it to download its stored temperatureinformation to another system such as a supervisory computer or patientmonitor. The way in which such a feature is implemented is known. Theway in which such temperature values, time-stamped or not, are storedfor one or more patients and then recalled for viewing on a display isalso well known.

Several different embodiments of the invention have been describedabove. It should be understood, however, that these are merelyillustrative. The invention is not to be limited to the particular formsor methods disclosed; rather, the invention is to cover allmodifications, equivalents and alternatives falling within the scope ofthe following claims.

1-20. (canceled)
 21. A device for measuring a temperature of atemperature medium of a patient, the device comprising: an access deviceinsertable into the patient at a location of the temperature medium, theaccess device including an outer wall and at least one thermal massother than the temperature medium, wherein the thermal mass is locatedwithin a thermal lumen defined in the access device; a carrierconfigured to extend through a carrier lumen of the access device; and atemperature sensor supported by the carrier; wherein a port is definedin the outer wall of the access device in direct communication with thecarrier lumen and the carrier is configured to position the temperaturesensor proximal to the port to allow direct contact of the temperaturemedium with the temperature sensor.
 22. A device of claim 21, whereinthe carrier is positioned between the temperature sensor and the thermalmass so as to insulate the temperature sensor from the thermal mass. 23.A device of claim 21, wherein the port is larger than the temperaturesensor and the carrier is configured to position the temperature sensorsubjacent and within the port, allowing the temperature sensor to besubstantially surrounded by and in direct contact with the temperaturemedium.
 24. A device of claim 21, wherein the temperature sensor ismounted to the carrier by a thermally stable adhesive.
 25. A device ofclaim 21, wherein the a distal end of the carrier is configured toextend out of the opening.
 26. A device of claim 25, wherein the distalend of the carrier is further configured to bend back along the outerwall and away from a direction of insertion.
 27. A device of claim 21,wherein a signal wire extends from the temperature sensor and at leastpartially along the carrier.
 28. A device of claim 21, wherein thecarrier is configured to extend out of the port past the outer wall soas to position the temperature sensor in the temperature meeting.
 29. Adevice of claim 28, wherein the carrier is biased to extend out of theport.
 30. A device of claim 29, wherein the carrier is biased to form anelbow joint.
 31. A device of claim 30, wherein a signal wire isconnected to the sensor and is also configured to form the elbow joint.32. A device of claim 31, further comprising an adhesive compoundextending over the sensor so as to keep the carrier and signal wirestraight until dissolved by contact with the temperature medium.
 33. Adevice of claim 28, wherein the carrier is a short tubular member thatcontains the thermal sensor.
 34. A device of claim 33, wherein thetubular member has ends anchored within the access device and a middleportion extending through the port.
 35. A device of claim 34, whereinthe tubular member forms a loop with respect to the access device.
 36. Adevice of claim 35, wherein the tubular member is configured to extendstraight within the carrier lumen during insertion of the access devicewithin the patient.
 37. A device of claim 27, wherein the signal wireincludes a substantially right angle bend adjacent the temperaturesensor.
 38. A device of claim 21, wherein the carrier is a signal wireconnected to the temperature sensor.
 39. A device of claim 38, whereinthe temperature sensor is supported within the port by an adhesivecompound.
 40. A method of measuring a temperature of a temperaturemedium of a patient, the method comprising: inserting an access deviceinto the patient at a location of the temperature medium; positioning acarrier supporting a temperature sensor in a carrier lumen of the accessdevice until the temperature sensor is proximal to a port defined in anouter wall of the access device; and directly contacting the temperaturemedium through the port with the temperature sensor and measuring thetemperature of the temperature medium.
 41. A device for measuring atemperature of a temperature medium of a patient, the device comprising:an access device insertable into the patient at a location of thetemperature medium, the access device including an outer wall and atleast one thermal mass other than the temperature medium wherein thethermal mass is located within a thermal lumen defined in the accessdevice; a temperature sensor supported on the outer wall of the accessdevice so as to directly contact the temperature medium; and a signalwire connected to the temperature sensor and extending through anopening in the outer wall, into the access device and away from thepatient within the access device.
 42. A device of claim 41, furthercomprising an adhesive compound securing the temperature sensor to theaccess device.
 43. A device for measuring a temperature of a temperaturemedium of a patient, the device comprising: an access device insertableinto the patient at a location of the temperature medium, the accessdevice including at least one thermal mass other than the temperaturemedium wherein the thermal mass is located within a thermal lumendefined in the access device; a temperature sensor; and an tip affixedto a distal end of the access device for positioning within thetemperature medium and including an opening extending therethrough intocommunication with the thermal lumen, wherein the tip is comprised of aninsulative material and supports the temperature sensor.
 44. A device ofclaim 43, wherein the tip includes a split extending between the openingand the temperature sensor.
 45. A device of claim 44, wherein a portionof the tip supporting the temperature sensor is configured to separatealong the split from another portion of the tip through which theopening extends.